I’m just about finished refurbishing a Heathkit SB-401 amateur
transmitter that has, according to the manual’s parts list, five 0.2uF
“resin” capacitors. What are these things and how reliable are they?
Does conventional wisdom dictate that such caps should be replaced?

I’ve searched the web for information on this, but only get hits
concerning Black Beauty caps, which most always need to be replaced.

-Dave Drumheller, K3WQ

What do they look like?

The article at http://antiqueradio.org/recap.htm has pictures of the common
capacitor types.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

wrote:
I=92m just about finished refurbishing a Heathkit SB-401 amateur
transmitter that has, according to the manual=92s parts list, five 0.2uF
=93resin=94 capacitors. What are these things and how reliable are they?
Does conventional wisdom dictate that such caps should be replaced?

They are called "resin-dipped" because of the outer casing. You don't really
care about the outer casing, you care about what is inside. If the dielectric
is plastic, keep it. If it's paper, replace it.

I=92ve searched the web for information on this, but only get hits
concerning Black Beauty caps, which most always need to be replaced.

Where are the caps and what will happen if they fail? In a receiver IF,
a bad cap can take out an IF transformer, but if it's just driving another
tube stage, the consequences of failure are minimal.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

On May 22, 10:51*am, "Phil Nelson" wrote:
What do they look like?

The article athttp://antiqueradio.org/recap.htmhas pictures of the common
capacitor types.

Phil Nelson
Phil's Old Radioshttp://antiqueradio.org/index.html

They're bulbous, and look very much like the contemporary orange drop
capacitor we all know and love.

-Dave

On May 22, 11:07*am, (Scott Dorsey) wrote:
wrote:
I=92m just about finished refurbishing a Heathkit SB-401 amateur
transmitter that has, according to the manual=92s parts list, five 0.2uF
=93resin=94 capacitors. *What are these things and how reliable are they?
Does conventional wisdom dictate that such caps should be replaced?

They are called "resin-dipped" because of the outer casing. *You don't really
care about the outer casing, you care about what is inside. *If the dielectric
is plastic, keep it. *If it's paper, replace it.

I=92ve searched the web for information on this, but only get hits
concerning Black Beauty caps, which most always need to be replaced.

Where are the caps and what will happen if they fail? *In a receiver IF,
a bad cap can take out an IF transformer, but if it's just driving another
tube stage, the consequences of failure are minimal. *
--scott
--
"C'est un Nagra. *C'est suisse, et tres, tres precis."

Three are used in the detector for the automatic level control (ALC)
circuit. Failure here probably wouldn’t be catastrophic. Another
provides bypass in the output driver grid circuit, but is shunted by
some large resistors. I doubt failure would do much here either. The
last one provides bypass on the filament voltage to the linear master
oscillator (LMO). In this case, failure as a short could stress the
power transformer.

-Dave, K3WQ

"Scott Dorsey" wrote in message
...
wrote:
I=92m just about finished refurbishing a Heathkit SB-401
amateur
transmitter that has, according to the manual=92s parts
list, five 0.2uF
=93resin=94 capacitors. What are these things and how
reliable are they?
Does conventional wisdom dictate that such caps should be
replaced?

They are called "resin-dipped" because of the outer
casing. You don't really
care about the outer casing, you care about what is
inside. If the dielectric
is plastic, keep it. If it's paper, replace it.

I=92ve searched the web for information on this, but only
get hits
concerning Black Beauty caps, which most always need to be
replaced.

Where are the caps and what will happen if they fail? In
a receiver IF,
a bad cap can take out an IF transformer, but if it's just
driving another
tube stage, the consequences of failure are minimal.
--scott
--

I'm not so sure paper dielectric caps are automatically
so bad. The key is to measure the cap, see if the capacity
is near what its supposed to be and if its lossy.
The casing can have an effect. For instance, the
notorious Black Beauty caps are often found with cracks or
even bits of the case cracked off. These have exactly the
same dielectric and construction as the Orange Drop caps,
namely paper impregnated with a plastic, the difference is
that the BBs are molded resin, not sure of what it is, and
the ODs are dipped Epoxy. OD's are pretty reliable where at
least early BBs are trouble. I think the problem with the
BBs has to do with moisture leaking into the body of the cap
but also the winding in the ones I've dissected were
distorted, perhaps by shrinkage. Curiously, BBs were sold
originally as deluxe capacitors for long life and operation
over an extended temperature range.
Old waxed paper caps should be checked but I've found
plenty which were still good. In general, where a paper cap
is used well under its maximum voltage rating it will have
long life.
The effect of a decoupling cap going bad may be to cause
feedback or to short the power to the element. They are
almost always used with a resistor to form an RC filter. I
don't see how a bad decoupling cap could take out an IF
transformer because its ahead of the transformer and will
not draw current through it. A bad coupling cap can put bias
onto the following tube grid (or transistor) causing high
distortion or other problems. Where an audio amp has
unusually high distortion coupling caps are always at the
top of the list of suspects. Coupling caps should have the
lowest leakage obtainable.
I would check the suspect caps with a bridge, or even
just with an ohm meter, to see if they should be replaced.
If they are not bad just leave them alone.


--
---
Richard Knoppow
Los Angeles, CA, USA

wrote in message
...
On May 22, 11:07 am, (Scott Dorsey) wrote:
wrote:
I=92m just about finished refurbishing a Heathkit SB-401 amateur
transmitter that has, according to the manual=92s parts list, five 0.2uF
=93resin=94 capacitors. What are these things and how reliable are they?
Does conventional wisdom dictate that such caps should be replaced?

They are called "resin-dipped" because of the outer casing. You don't
really
care about the outer casing, you care about what is inside. If the
dielectric
is plastic, keep it. If it's paper, replace it.

I=92ve searched the web for information on this, but only get hits
concerning Black Beauty caps, which most always need to be replaced.

Where are the caps and what will happen if they fail? In a receiver IF,
a bad cap can take out an IF transformer, but if it's just driving another
tube stage, the consequences of failure are minimal.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Three are used in the detector for the automatic level control (ALC)
circuit. Failure here probably wouldn’t be catastrophic. Another
provides bypass in the output driver grid circuit, but is shunted by
some large resistors. I doubt failure would do much here either. The
last one provides bypass on the filament voltage to the linear master
oscillator (LMO). In this case, failure as a short could stress the
power transformer.

-Dave, K3WQ

The leakage may only show when the cap is subjected to full
rated voltage. Chances are they will work in filament and
cathode bypass applications without much issue. They rarely
go into a zero ohm failure mode.

If it is part of the time constant for the ALC circuit, leakage
could cause big problems. What grid is it bypassing in the
driver stage--screen or control?

If they are mylar or polyester dielectric they are probably okay.
New caps are pretty cheap, however.

Pete

wrote:

Three are used in the detector for the automatic level control (ALC)
circuit. Failure here probably wouldn=92t be catastrophic. Another
provides bypass in the output driver grid circuit, but is shunted by
some large resistors. I doubt failure would do much here either. The
last one provides bypass on the filament voltage to the linear master
oscillator (LMO). In this case, failure as a short could stress the
power transformer.

I'd test them... if they seem okay in-circuit, leave them there. If down
the road one of them fails, replace them all.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."